Ceramic machine parts



March 5, 1957 FlG-1 H. H. E. SCHARF ET AL 2,783967 CERAMIC MACHINE. PARTS Filed Den. 24. 1952 FlG-2 IN VEN TORS HERBERT SCHARF,

RUDOLF SCHMUCKER 8u WALTER RICHTER United States Patent O F CERAMIC MACl-IINE PARTS Herbert H. E. Scharf, Rudolf W. F. Schmucker, and Walter Richter, Augsburg, Germany, assignors to Maschineufabrik Augsburg-Nurnberg A. G., Augsburg, Germany, a corporation of Germauy Application Deember 24, 1952, Seriell N0. 327,716

Claims priority, application Germany J anuary 3, 1952 3 Claims. (C1. 253-77) This invention relates to ceramic machine parts, and more particularly to the manufacture of ceramic turbine blades for mounting in a metal roter rirn.

Ceramic materials have been found appropriate for turbine blades and similar parts of high temperature gas turbines because cf the thermal properties of ceramics. Many ceramic materials, however, exhibit 10W mechanical strength despite their desirable thermal properties. Accordingly, special measures must be taken to increase the mechanical strength or stability ol: certain ceramic.

materials if it is desired to use them, for example, in high temperature gas turbine blades.

lt has been found that coating the ceramic material with a glaze substantially increases the tensile strength f the ceramic. At the same time, however, such a glaze notably increases the weight of the ceramic material. Such increased weight, particularly on the leaf or vane portion of a turbine blade, may not be desirable since it correspondingly increases the centrifugal force to which the blade is subjected as well as increasing the brittleness of the ceramic in the part of the blade which is most subjected to oscillation and vibration in operation cf the turbine.

It is accordingly a principal object of this invention to produce a turbine blade with a strength-increasing gbll'azde applied only to highly strained portions of the A further object of the invention is to apply a glaze the linear thermal expansion coefficient of which iS smaller than that of the blade material for increasing mechanical stability.

Another object of this invention is to provide a ceramic turbine blade with a stability-increasing glaze applied to but portions thereof and with the transition points between unglazed and glazed portions of the blade graduated.

A further object of this invention is to provide a cetamic turbine blade having on the root portions thereof rangaged by a metal turbine roter a layer of strengthmcreasing glaze and an additional layer of machinable material to provide fo1' close tolerance fitting cf said blades without disturbing surface equilibrium of said glaze or said blade.

Still another object of this invention is to provide a ceramic turbine blade with the root portions thereof carrying a strength-increasing glaze the amount of which is graduated at the transition point between glazed and unglazed portions of the blade.

Still another object cf this invention is to provide a ceramic turbine blade having 011 selected highly strained. portions thereof, such as the root portion seating surfaces and the thin trailing edge of the vane, a strength-increasing glaze with a lower coeflicient of thermal expansion than the cerarnic material from which the blade is formed.

Other objects and advantages will be apparent from the following description, and the appended claims.

In the drawing:

between the glazed root and the unglazed vane the thickness of the applied glaze decreases either gradually 01' stepwise. in at least two steps between the glazed root 10 and the unglazed vane 11. As a result of the internal conditions achieved in the firing of the ceramic material as well as the increased stability imparted to the glazed portion of the blade, the transition between glazed and unglazed portions might produce a point of weakness unless this transition were graduated.

'I'he vane portion 11 is unglazed to reduce the weight thereof subjected to centrifugal force as weil as to avoid excessive embrittlement cf the ceramic material of the vane portion 11 which is primarily subjected to'osizillation and vibrational forces in operation of tl1e turbine. Since, however, the trailing edge 13 of the vane portion may be quite thin, a thin strip of glaze is applied to this thin trailing edge to increase the mechanical strength thereof in use.

During the firing of tl1e blade the ceramic material acquires certain internal equilibrium conditions which are disruptable by such operations as machining the surface 0f th.e fired blade. Such machining operations am, bewever, frequently desirable on the blade root in Order to achieve close tolerance fit of the blade in the metal turbine roter. Accordingly, a further machinable layer 14 of ceramic material is applied over the seating surfaces cf the blade root as a machining allowance in order that necessary machining of the blade root may take place without disruption of the internal strength equilibria of the ceramic blade nor the surface' cf the strength incr :asing glaze. Also the glaze provides an insulating layer to protect the fired cerarnic from efiects of machining the layer 14.

The glaze is selected according to the ceramic material so that the coefficient of therrnal expansion of the glaze will be lass than that of the ceramic material thereby considerably increasing the strength cf the ceramic at high temperature condi-tions. The glaze is preferably formed 011 the glazed portion cf the ceramic blade during the firing cf the blade. By way of example, with a turbine blade formed primarily of the steatite-like materials a satisfactory glaze composition according to this invention comprises by way of example a glaze of the formula of Seger:

MgO 0,37 CaO 0,07 K20 0,50 MnO 0,06

Additionally a nonamorphous firing skin or a development glaze can be obtained on highly stressed portions of the ceramic article by placing on the article, for example, an alkali earth or alkali compound which melts at high temperatures and coats the surface of the ceramic blade with a uniform thin layer. Satisfactory results have been obtained by forming such a firing skin, development glaze and the glaze according to this invention on selected portions of the ceramic blade during the final firing thereof to achieve optimum internal equilibrium conditions.

Tl1us it Will be seen that this invention provides a turbine blade in which selected highly strained portions are Si0z 8,60 A12O3 0,94

Patented Mal. 5, 1957 Preferably this graduated thickness decreases strengthened by the adition cf a special glaze material, but with other portions cf the blade free of glaze and accordingly unencumbered by either the added weight Q1 added embritflment which*a g1aza provides. Also, p8tticiulafly on the machined root portions of1he blade, the internal equilibria of the ceramip material are insulated by the glazc by disruption during machining operations, and points of possible weakness at the transition area b etwee u glazed and unglazed portions a1'e avqided by ste pwise graduation cf glaze thickness.

While the method and product herein dessribcd ccn stitute pre ferred embodiments of the inyention, it is to be understood that the inve ntion is 1101 limited to this precise method and prodct, and that qhanges may be made -therein without depa;ting from t11e scope of the inv e ntion which is 'dfififld in the appended claims.

Whatis claimed is:

1, A turbine blade of fired cerami c material having a veme portion and a r0ot portion adapted for mounting in a metal turbine rotor comprising a surface layer cf glaze in said root portion o nly, said vane portion being substantially free of glazc, and a se c ond surface Iayer of glaze of less thickness than said first layer between said root portion and said vane portion effecting gradual dimunition cf glaze thickness, the coefficient cf thermal expansion of said glaze being less than that cf said ceramic material.

2. ceramic turbine blade according to claim 1 having an additiorial layer cf glaze in the form of a thinstrip along the trailing edge of said vane portion.

3. A ceramic turbine blade according to claim 1 in which said decrease of gilazed layer thickness from said root portion ;oward said vane portion occ urs in at least two stages.

References Citd in the file of this patent UNI-'TED STATES PATENTS 1,081,542 Malm Dec. 16, 1913 2,157,100 Rowland May 9, 1939 2320,099 Ramsay et a1. May 25, 1943 2431660 Gaudenz'i'-----'. Nov. 25, 1947 2,531252 Goetze1et a1. Q. Jan. 1, 1952 2683,018 Schorner July 6, 1954 FOREIGN PATENTS 195,050 Great Britain July 19, 1923 664,986 Great Britain Jan. 16, 1952 821,735 Germany Nov. 19, 1951 892,785 France Jan. 13, 1944 OTHER REFERENCES Sex. N0. 385,334, Schutte (A. P. C.) publishe-d May 

1. A TURBINE BLADE OF FIRED CERAMIC MATERIAL HAVING A VANE PORTION AND A ROOT PORTION ADAPTED FOR MOUNTING IN A METAL TURBINE ROTOR COMPRISING A SURFACE LAYER OF GLAZE ON SAID ROOT PORTION ONLY, SAID VANE PORTION BEING SUBSTANTIALLY FREE OF GLAZE, AND A SECOND SURFACE LAYER OF GLAXE OF LESS THICKNESS THAN SAID FIRST LAYER BETWEEN SAID ROOT PROTION AND SAID VANE PORTION EFFECTING GRADUAL DIMUNITION OF GLAZE THICKNESS, THE COEFFICIENT OF THERMAL EXPANSION OF SAID GLAZE BEING LESS THAN THAT OF SAID CERAMIC MATERIAL. 